In 2003, American Antigravity participated in a joint-proposal for the Naval Research Lab to showcase their newest breakthrough in Lifter research- a low-voltage technique to providing mega-thrust comparable to an aircraft or helicopter! 

This unique videoclip is a demonstration of their 4-foot Lifter and a good narrative overview of how it all works.

More technical info: 

Ion wind, ionic wind, or coronal wind is a stream of ionized fluid generated by a strong electric field.

Electric charges on conductors reside entirely on their external surface (see Faraday cage), and tend to concentrate more around sharp points and edges than on flat surfaces. 

This means that the electric field generated by charges on a sharp conductive point is much stronger than the field generated by the same charge residing on a large smooth spherical conductive shell. 

When this electric field strength exceeds what is known as the corona discharge inception voltage (CIV) gradient, it ionises the air about the tip, and a small faint purple jet of plasma can be seen in the dark on the conductive tip. Ionisation of the nearby air molecules result in generation of ionised air molecules having the same polarity as that of the charged tip. 

Subsequently, the tip repels the like-charged ion cloud, and the ion cloud immediately expands due to the repulsion between the ions themselves. This repulsion of ions creates an electric "wind" that emanates from the tip, which is usually accompanied by a hissing noise due to the change in air pressure at the tip.

Unlike the functionality of the Electrohydrodynamic (EHD) thruster, the net force generated by an ion wind device does not rely on the momentum transfer between the charged and the neutral air molecules, but only on the impulse that the charged ions gain during their repulsion from the tip. 

It is analogous to recoil of a gun when it fires a bullet. Due to this property, ion impulse devices may find use in spacecraft propulsion, even though ion wind forces are much smaller than those of an EHD thruster operated in air.

 

The Biefeld–Brown effect is an effect that was discovered by Thomas Townsend Brown (USA) and Dr. Paul Alfred Biefeld (CH). The effect is more widely referred to as electrohydrodynamics (EHD) or sometimes electro-fluid-dynamics, a counterpart to the well-known magneto-hydrodynamics. 

Extensive research was performed during the 1950's and 1960's on the use of this electric propulsion effect. During 1964, Major De Seversky had in fact published a lot of his related work in U.S. Patent 3,130,945, and with the aim to forestall any possible misunderstanding about these devices, had termed these flying machines as ionocrafts. 

In the following years, many promising concepts had to be abandoned and forgotten due to the technological limitations, but at the same time, science has advanced a lot in the EHD field. 

The effect has only recently become popular again and such flying devices are now known as EHD thrusters. Simple single-stage versions lifted by this effect are sometimes also called 'lifters'.

Effect Analysis:

The effect relies on corona discharge, which allows air molecules to become ionised near sharp points and edges. Usually, two electrodes are used with a high voltage between them, ranging from a few kilovolts and up to megavolt levels, where one electrode is small or sharp, and the other larger and smoother. 

The most effective distance between electrodes occurs at an electric field gradient of about 10 kV/cm, which is just below the nominal breakdown voltage of air between two sharp points, at a current density level usually referred to as the saturated corona current condition. 

This creates a high field gradient around the smaller, positively charged electrode. Around this electrode, ionisation occurs, that is, electrons are stripped off the atoms in the surrounding medium, they are literally pulled right off by the electrode's charge.

This leaves a cloud of positively charged ions in the medium, which are attracted to the negative smooth electrode, where they are neutralized again. 

In the process, thousands of impacts occur between these charged ions and the neutral air molecules in the air gap, causing a transfer in momentum between the two, which creates a net directional force on the electrode setup. 

This effect can be used for propulsion (see EHD thruster), fluid pumps and recently also in EHD cooling systems. 


Source: Wikipedia